Aluminum alloy cables have not been used for a long time in China, but there have been cases indicating that there are huge hidden dangers and risks in the application of aluminum alloy cables in cities and factories and mines. Below are two actual cases and eight factors that lead to risk accidents of aluminum alloy cables.

Case 1

A steel factory used aluminum alloy cables in bulk, but two major fires occurred within a year of production, resulting in a half month shutdown and a direct economic loss of 200 million yuan.

Case 2

An aluminum alloy cable was used in the lighting distribution system of a certain city in Hunan. Within one year after installation, strong corrosion of the aluminum alloy cable occurred, resulting in damage to the cable joints and conductors, and power outage of the line.

Through these two cases, it can be seen that the large-scale promotion of aluminum alloy cables in Chinese cities and factories has left hidden dangers for cities and factories. Users lack understanding of the basic performance of aluminum alloy cables, resulting in huge losses. If users learn about the characteristics of aluminum alloy cables in terms of fire reliability and anti-corrosion issues in advance, such losses can be avoided in advance.

From the characteristics of aluminum alloy cables, they have natural defects in fire prevention and corrosion prevention. It is manifested in the following 8 aspects:

1. Corrosion resistance, 8000 series aluminum alloys are not as good as regular aluminum.

According to Note 4 of Table 1 of the GB/T19292.2-2003 standard, the corrosion resistance of aluminum alloys is worse than that of ordinary aluminum and worse than that of copper. This is because aluminum alloy cables add magnesium, copper, zinc, and iron elements, making them prone to local corrosion such as stress corrosion fracture, layer corrosion, and intergranular corrosion. Moreover, the 8000 series of aluminum alloys belong to corrosion-prone formulas. Aluminum alloy cables have added heat treatment processes, which can cause uneven physical states and are more prone to corrosion than aluminum cables. Currently, the aluminum alloys used in China are mostly 8000 aluminum alloy series.

2. The temperature resistance of aluminum alloys is significantly different from that of copper.

The melting point of copper is 1080 ℃, while the melting point of aluminum and aluminum alloys is 660 ℃, so copper conductors are a better choice for fire-resistant cables. Some aluminum alloy cable manufacturers now claim to be able to produce fire-resistant aluminum alloy cables and have passed relevant national standard tests. However, there is no difference between aluminum alloy cables and aluminum cables in this regard. If they are in the center of a fire, i.e. when the temperature is higher than the melting point of aluminum alloy and aluminum cable, regardless of the insulation measures taken, the cable will melt in a short period of time and lose its conductive function. Therefore, aluminum and aluminum alloy are not suitable as fire-resistant cable conductors, It is also not suitable for use in densely populated urban power distribution networks, buildings, factories and mines.

3. The thermal expansion coefficient of aluminum alloy is much higher than that of copper, and AA8030 aluminum alloy is even higher than ordinary aluminum.

The thermal expansion coefficient of aluminum is much higher than that of copper, and aluminum alloys AA1000 and AA1350 have slightly improved, while AA8030 is even higher than aluminum. High coefficient of thermal expansion will lead to poor contact of conductors after Thermal expansion and a vicious cycle. However, the power supply always has a peak valley difference, which poses a huge challenge to cable performance.

4. Aluminum alloys have not solved the problem of aluminum oxidation.

Aluminum alloy or aluminum exposed to the atmosphere will quickly form a hard, strong bonding but fragile thin film with a thickness of approximately 10nm, which has a high electrical resistivity. Its hardness and bonding force make it difficult to form conductive contacts, which is why the surface oxide layer must be removed before installation of aluminum and aluminum alloys. The surface of copper also oxidizes, but the oxide layer is soft and easily breaks down into semiconductors under stress, forming metal metal contact.

5. Aluminum alloy cables have improved stress relaxation and creep resistance, but they are far inferior to copper.Adding specific elements to ordinary aluminum can improve its creep performance, but the degree of improvement is also very limited compared to ordinary aluminum, and there is still a huge gap compared to copper. Moreover, whether aluminum alloy cables can truly improve creep resistance is closely related to the process, technology, and quality control level of each enterprise. This uncertainty is itself a risk factor, and without strict control of mature processes, improving creep performance of aluminum alloy cables cannot be guaranteed.

6. Aluminum alloy cables have not solved the reliability issue of aluminum connections.

There are 5 factors that affect the reliability of aluminum connections, and aluminum alloys have only improved on one issue and have not solved the problem of common aluminum connections. There are five issues with the connection of ordinary aluminum. The 8000 series aluminum alloy has only improved in terms of creep and stress relaxation, and there has been no improvement in other aspects. Therefore, the connection problem will still be a major issue affecting the quality of aluminum alloys. Aluminum alloy is also a type of aluminum and is not a new material. In terms of conductor performance, if the gap between aluminum's basic performance and copper is not solved, aluminum alloy cannot replace copper.

7. Inconsistent quality control of domestic aluminum alloys (alloy composition) leads to poor creep resistance.

After POWERTECH testing in Canada, it was found that the composition control of domestic aluminum alloys is unstable. The Si content of North American aluminum alloy cables varies by less than 5%, while the Si content of domestic aluminum alloys varies by 68%. Si is an important element that affects creep performance. That is to say, domestic aluminum alloy cables have not yet formed a mature process in terms of creep resistance.

8. The process of aluminum alloy cable joints is complex and prone to hidden dangers.

The aluminum alloy cable joint process has three more processes than copper cable, and the effective removal of the oxide layer and coating of antioxidants are key. The domestic construction level and quality requirements are uneven, leaving hidden dangers. Moreover, due to the lack of a strict legal liability compensation system in China, the ultimate consequences of losses in practice are mostly borne by users themselves.

In addition to the above factors, aluminum alloy cables also have a series of professional issues, such as lack of unified standards for cutoff flow, inadequate joint terminals, increased capacitive current, narrowing or insufficient support of aluminum alloy cable laying spacing due to increased cross-section, construction difficulties caused by increased cable cross-section, whether the cable trench # space is matched, sharp increase in maintenance and risk costs, increased full life cycle costs, and designers without standards to follow, Improper handling or intentional neglect of any of these items is sufficient to cause users to suffer significant and irreparable losses and accidents.

Article source: Internet